1. Field of the Invention
This invention relates to improvement of magnetic properties of glassy metal alloys and, more particularly, to heat treatment of toroidally wound cores of filaments of glassy metal alloys with or without an externally applied magnetic field.
2. Description of the Prior Art
Crystalline, high permeability 80% nickel/20% iron alloys achieve their outstanding magnetic properties as a result of cold reduction followed by an 1100.degree. C anneal in pure dry hydrogen. This high temperature makes it difficult to maintain dimensional tolerances. Moreover, objects of irregular shape must be coated with a ceramic (usually aluminum oxide) to prevent pressure welding or sticking during heat treatment. Also important, parts must be carefully supported during heat treatment to prevent dimensional distortion. At temperatures above 600.degree. C, a protective atmosphere such as pure, dry (-70.degree. C dew point) hydrogen must be provided to eliminate the possibility of oxidation. A good vacuum (10.sup.-8 m or less) may be used as a substitute for hydrogen. However, this demands the use of a high temperature vacuum furnace.
Recently, studies have been reported concerning the magnetic annealing of a glassy metal alloy, Fe.sub.40 Ni.sub.40 P.sub.14 B.sub.6 (the subscripts are in atom percent); see Vol. 11, IEEE Transactions on Magnetics, pp. 1644-1649 (1975). Generally improved properties are indicated. However, it is also apparent that again either an inert atmosphere or high vacuum is required to anneal the alloy and thereby obtain the improved properties.
An economical, convenient process for heat treating toroidally wound cores of filaments of glassy metal alloys is required. Such a process requires a heat-transfer medium into which the cores may be suspended. The medium should be easy to use, easy to heat, require no complex apparatus and be able to withstand temperatures of at least 350.degree. C without thermally decomposing. Further, such a medium must not react with the alloy or form deleterious contamination products thereon. The medium must also be an electrical insulator in order to minimize its bypassing of any magnetizing current applied for directionalizing during heat treatment.